For example, an inverter has three current paths, and outputs a three-phase AC voltage to a three-phase load. Each of the current paths has a pair of switch devices on a high-potential side and a low-potential side of a DC voltage, respectively. Each of the switch devices carries out switching based on a switching pattern decided based on a result of comparing a carrier value with a signal wave value. The three-phase AC voltage is output based on this switching.
An example of a power converting apparatus includes an indirect matrix converter having a current-source converter, a voltage-source inverter, and a DC link for connecting the converter and the inverter. In the indirect matrix converter, the DC voltage is applied to the DC link, but the DC link does not have a smoothing circuit.
The current-source converter generates so-called commutation for switching the current paths through switching, and converts an alternating current into the DC voltage. In order to reduce loss at the time of switching by the current-source converter, so-called zero-current switching for applying no currents to the current-source converter at the time of switching is proposed.
In order to prevent a current from being applied to the current-source converter, the DC link is insulated from the three-phase load in the voltage-source inverter. Particularly in a case where the three-phase load is an electric motor, the three-phase load is short-circuited in order to return a current caused by a counter-electromotive force of the electric motor. Such an operation of the voltage-source inverter is realized by employing a switching pattern based on a voltage vector generally called a zero voltage vector.